From nobody Sun May 24 22:42:29 2026 Received: from cstnet.cn (smtp81.cstnet.cn [159.226.251.81]) (using TLSv1.2 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 700AE32B128; Thu, 21 May 2026 02:28:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=159.226.251.81 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779330526; cv=none; b=boxQMpqVegMP/22VvYqhFOKLMACEQ2iIMitTDScla/AlwyzxXcHuXJvaLGIvye55FBKT+wesQvXKbp2Tcbypy+BGNFAMlcAIvMlPSu/tnAlhWycBgCl4NRCPxtoQOikDvSB4CULY/g9s+64iLIcNzWbKnyYkizRKBIrs97S7EaA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779330526; c=relaxed/simple; bh=2Zf7B87TeFVRsACMrgdCHe3KYO/jbVY+kxl1WDKWFW8=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=gOlUZVbcaTCaXtgPkdl97A7zeIzumTYD4cCr1bordAmlw5eBZSWcxXT4UPM9ewZI5P2Tj8ozKybKYwZBw1bIZTIud4cpDBB+doeDl+fydW0RiOTrgOgyXp6zgeJFWMjSj0PUWI/FFn3d/WhGIDmUjuIkmsQ+b5j32raHsOBo0jA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=iscas.ac.cn; spf=pass smtp.mailfrom=iscas.ac.cn; arc=none smtp.client-ip=159.226.251.81 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=iscas.ac.cn Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=iscas.ac.cn Received: from localhost.localdomain (unknown [111.196.245.140]) by APP-03 (Coremail) with SMTP id rQCowACHa+LKbQ5qmbHAEQ--.571S2; Thu, 21 May 2026 10:28:26 +0800 (CST) From: Pengpeng Hou To: Nathan Chancellor , Nicolas Schier , Masahiro Yamada Cc: Jonathan Corbet , Shuah Khan , linux-kbuild@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Pengpeng Hou Subject: [PATCH v2] kconfig: add optional warnings for changed input values Date: Thu, 21 May 2026 10:28:24 +0800 Message-ID: <20260521022824.38591-1-pengpeng@iscas.ac.cn> X-Mailer: git-send-email 2.50.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-CM-TRANSID: rQCowACHa+LKbQ5qmbHAEQ--.571S2 X-Coremail-Antispam: 1UD129KBjvJXoW3CryDWF18Kw43Wr4fZF15XFb_yoWktFW3pa yrA345KF4kJFn3ta1Utas7WF1rurn7WrW5GF1jqw1UAF90yrWIyrsrKw1Yyry3u39FyFW5 AFyFgF4FyF1UAaUanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUkC14x267AKxVW8JVW5JwAFc2x0x2IEx4CE42xK8VAvwI8IcIk0 rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2ocxC64kIII0Yj41l84x0c7CEw4AK67xGY2AK02 1l84ACjcxK6xIIjxv20xvE14v26ryj6F1UM28EF7xvwVC0I7IYx2IY6xkF7I0E14v26r4j 6F4UM28EF7xvwVC2z280aVAFwI0_Cr1j6rxdM28EF7xvwVC2z280aVCY1x0267AKxVWxJr 0_GcWle2I262IYc4CY6c8Ij28IcVAaY2xG8wAqx4xG64xvF2IEw4CE5I8CrVC2j2WlYx0E 2Ix0cI8IcVAFwI0_JrI_JrylYx0Ex4A2jsIE14v26r1j6r4UMcvjeVCFs4IE7xkEbVWUJV W8JwACjcxG0xvY0x0EwIxGrwACjI8F5VA0II8E6IAqYI8I648v4I1lc7CjxVAaw2AFwI0_ Jw0_GFyl42xK82IYc2Ij64vIr41l4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2IqxVAqx4xG67 AKxVWUJVWUGwC20s026x8GjcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v26r1q6r43MIIY rxkI7VAKI48JMIIF0xvE2Ix0cI8IcVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6xkF7I0E14 v26r4j6F4UMIIF0xvE42xK8VAvwI8IcIk0rVWUJVWUCwCI42IY6I8E87Iv67AKxVWUJVW8 JwCI42IY6I8E87Iv6xkF7I0E14v26r4j6r4UJbIYCTnIWIevJa73UjIFyTuYvjfUFg4SDU UUU X-CM-SenderInfo: pshqw1xhqjqxpvfd2hldfou0/ Content-Type: text/plain; charset="utf-8" When reading .config input, Kconfig stores user-provided values first and then resolves the final value after applying dependencies, ranges, and other constraints. If the final value differs from the user's input, Kconfig already tracks that state internally, but it does not provide any focused diagnostic to show which explicit inputs were adjusted. This is particularly confusing for requested values that get forced down by unmet dependencies or clamped by ranges. Add an opt-in diagnostic controlled by KCONFIG_WARN_CHANGED_INPUT. Emit the warnings from conf_write() and conf_write_defconfig() after value resolution and through the existing message callback path so the default behavior stays unchanged and interactive frontends remain usable. Avoid the conf_message() formatting buffer for this diagnostic so long warning lists are not truncated before reaching the callback, and mark processed symbols as written before the SYMBOL_WRITE check so duplicate menu nodes cannot emit duplicate warnings. Document the new environment variable and add tests for both olddefconfig and savedefconfig. Signed-off-by: Pengpeng Hou Reviewed-by: Nicolas Schier Tested-by: Nicolas Schier --- Changes since v1: https://lore.kernel.org/all/20260406233001.1-kconfig-warn= -changed-input-pengpeng@iscas.ac.cn/ - rename "found" to "changed_input_found" as suggested by Nicolas - avoid the conf_message() 4096-byte formatting buffer so long warning lists are not truncated before the callback sees them - mark each processed symbol as SYMBOL_WRITTEN before checking SYMBOL_WRITE to avoid duplicate warnings for duplicate menu nodes - add duplicate-definition selftest coverage - do not carry the Reviewed-by/Tested-by tags because v2 changes warning emission and duplicate suppression Documentation/kbuild/kconfig.rst | 5 + scripts/kconfig/confdata.c | 107 +++++++++++++++++- .../kconfig/tests/warn_changed_input/Kconfig | 40 +++++++ .../tests/warn_changed_input/__init__.py | 27 +++++ .../kconfig/tests/warn_changed_input/config | 3 + .../tests/warn_changed_input/expected_config | 6 + .../warn_changed_input/expected_defconfig | 1 + .../tests/warn_changed_input/expected_stdout | 4 + 8 files changed, 189 insertions(+), 4 deletions(-) create mode 100644 scripts/kconfig/tests/warn_changed_input/Kconfig create mode 100644 scripts/kconfig/tests/warn_changed_input/__init__.py create mode 100644 scripts/kconfig/tests/warn_changed_input/config create mode 100644 scripts/kconfig/tests/warn_changed_input/expected_config create mode 100644 scripts/kconfig/tests/warn_changed_input/expected_defco= nfig create mode 100644 scripts/kconfig/tests/warn_changed_input/expected_stdout diff --git a/Documentation/kbuild/kconfig.rst b/Documentation/kbuild/kconfi= g.rst index d213c4f599a4..e35dd1d5f9d3 100644 --- a/Documentation/kbuild/kconfig.rst +++ b/Documentation/kbuild/kconfig.rst @@ -59,6 +59,11 @@ Environment variables for ``*config``: This environment variable makes Kconfig warn about all unrecognized symbols in the config input. =20 +``KCONFIG_WARN_CHANGED_INPUT`` + If set to a non-blank value, Kconfig prints optional warnings for + user-provided values that change after Kconfig resolves dependencies + or applies other constraints such as ranges. + ``KCONFIG_WERROR`` If set, Kconfig treats warnings as errors. =20 diff --git a/scripts/kconfig/confdata.c b/scripts/kconfig/confdata.c index 9599a0408862..1fe6d3644e79 100644 --- a/scripts/kconfig/confdata.c +++ b/scripts/kconfig/confdata.c @@ -206,6 +206,79 @@ static void conf_message(const char *fmt, ...) va_end(ap); } =20 +static void conf_message_raw(const char *s) +{ + if (conf_message_callback) + conf_message_callback(s); +} + +static bool conf_warn_changed_input_enabled(void) +{ + const char *env =3D getenv("KCONFIG_WARN_CHANGED_INPUT"); + + return env && *env; +} + +static const char *sym_get_user_value_string(struct symbol *sym) +{ + switch (sym->type) { + case S_BOOLEAN: + case S_TRISTATE: + switch (sym->def[S_DEF_USER].tri) { + case yes: + return "y"; + case mod: + return "m"; + default: + return "n"; + } + default: + return sym->def[S_DEF_USER].val ?: ""; + } +} + +static bool sym_user_value_changed(struct symbol *sym) +{ + if (!sym_has_value(sym) || sym->type =3D=3D S_UNKNOWN) + return false; + + switch (sym->type) { + case S_BOOLEAN: + case S_TRISTATE: + return sym->def[S_DEF_USER].tri !=3D sym_get_tristate_value(sym); + default: + return strcmp(sym_get_user_value_string(sym), + sym_get_string_value(sym)); + } +} + +static void conf_clear_written_flags(void) +{ + struct symbol *sym; + + for_all_symbols(sym) + sym->flags &=3D ~SYMBOL_WRITTEN; +} + +static void conf_append_changed_input_warning(struct gstr *gs, + struct symbol *sym, + bool *changed_input_found) +{ + if (!sym_user_value_changed(sym)) + return; + + if (!*changed_input_found) { + str_printf(gs, + "warning: user-provided values changed by Kconfig:\n"); + *changed_input_found =3D true; + } + + str_printf(gs, " %s%s: %s -> %s\n", + CONFIG_, sym->name, + sym_get_user_value_string(sym), + sym_get_string_value(sym)); +} + const char *conf_get_configname(void) { char *name =3D getenv("KCONFIG_CONFIG"); @@ -759,11 +832,15 @@ int conf_write_defconfig(const char *filename) { struct symbol *sym; struct menu *menu; + struct gstr gs; FILE *out; + bool warn_changed_input =3D conf_warn_changed_input_enabled(); + bool changed_input_found =3D false; =20 out =3D fopen(filename, "w"); if (!out) return 1; + gs =3D str_new(); =20 sym_clear_all_valid(); =20 @@ -772,10 +849,14 @@ int conf_write_defconfig(const char *filename) =20 sym =3D menu->sym; =20 - if (!sym || sym_is_choice(sym)) + if (!sym || sym_is_choice(sym) || sym->flags & SYMBOL_WRITTEN) continue; =20 sym_calc_value(sym); + if (warn_changed_input) + conf_append_changed_input_warning(&gs, sym, + &changed_input_found); + sym->flags |=3D SYMBOL_WRITTEN; if (!(sym->flags & SYMBOL_WRITE)) continue; sym->flags &=3D ~SYMBOL_WRITE; @@ -798,6 +879,13 @@ int conf_write_defconfig(const char *filename) print_symbol_for_dotconfig(out, sym); } fclose(out); + + conf_clear_written_flags(); + + if (changed_input_found) + conf_message_raw(str_get(&gs)); + + str_free(&gs); return 0; } =20 @@ -809,7 +897,10 @@ int conf_write(const char *name) const char *str; char tmpname[PATH_MAX + 1], oldname[PATH_MAX + 1]; char *env; + struct gstr gs; bool need_newline =3D false; + bool warn_changed_input =3D conf_warn_changed_input_enabled(); + bool changed_input_found =3D false; =20 if (!name) name =3D conf_get_configname(); @@ -838,6 +929,7 @@ int conf_write(const char *name) } if (!out) return 1; + gs =3D str_new(); =20 conf_write_heading(out, &comment_style_pound); =20 @@ -859,13 +951,16 @@ int conf_write(const char *name) } else if (!sym_is_choice(sym) && !(sym->flags & SYMBOL_WRITTEN)) { sym_calc_value(sym); + if (warn_changed_input) + conf_append_changed_input_warning(&gs, sym, + &changed_input_found); + sym->flags |=3D SYMBOL_WRITTEN; if (!(sym->flags & SYMBOL_WRITE)) goto next; if (need_newline) { fprintf(out, "\n"); need_newline =3D false; } - sym->flags |=3D SYMBOL_WRITTEN; print_symbol_for_dotconfig(out, sym); } =20 @@ -892,8 +987,12 @@ int conf_write(const char *name) } fclose(out); =20 - for_all_symbols(sym) - sym->flags &=3D ~SYMBOL_WRITTEN; + conf_clear_written_flags(); + + if (changed_input_found) + conf_message_raw(str_get(&gs)); + + str_free(&gs); =20 if (*tmpname) { if (is_same(name, tmpname)) { diff --git a/scripts/kconfig/tests/warn_changed_input/Kconfig b/scripts/kco= nfig/tests/warn_changed_input/Kconfig new file mode 100644 index 000000000000..69845e2f3fb3 --- /dev/null +++ b/scripts/kconfig/tests/warn_changed_input/Kconfig @@ -0,0 +1,40 @@ +# SPDX-License-Identifier: GPL-2.0 + +config DEP + bool "DEP" + help + Test dependency symbol for Kconfig warning coverage. + This is used by the warn_changed_input selftest. + It intentionally stays unset in the input fragment. + The test checks how dependent user input is adjusted. + +config A + bool "A" + depends on DEP + help + Test bool symbol for changed-input diagnostics. + The input fragment requests this symbol as built-in. + The unmet dependency on DEP forces the final value to n. + The warning should report that downgrade. + +config NUM + int "NUM" + range 10 20 + help + Test integer symbol for changed-input diagnostics. + The input fragment requests a value outside the allowed range. + Kconfig resolves it to the constrained in-range value. + The warning should report that adjustment. + +config DUP + bool "DUP" + depends on DEP + help + Test duplicate-definition handling for changed-input diagnostics. + The input fragment requests this symbol as built-in. + The duplicate definition below must not produce a duplicate warning. + This keeps the warning output stable for repeated menu entries. + +config DUP + bool + depends on DEP diff --git a/scripts/kconfig/tests/warn_changed_input/__init__.py b/scripts= /kconfig/tests/warn_changed_input/__init__.py new file mode 100644 index 000000000000..5a2b68fb1033 --- /dev/null +++ b/scripts/kconfig/tests/warn_changed_input/__init__.py @@ -0,0 +1,27 @@ +# SPDX-License-Identifier: GPL-2.0 +""" +Test optional warnings for user-provided values changed by Kconfig. + +Warnings should stay disabled by default, and should only appear when +KCONFIG_WARN_CHANGED_INPUT is enabled. +""" + + +def test(conf): + assert conf.olddefconfig('config') =3D=3D 0 + assert 'user-provided values changed by Kconfig' not in conf.stdout + + assert conf._run_conf('--olddefconfig', dot_config=3D'config', + extra_env=3D{ + 'KCONFIG_WARN_CHANGED_INPUT': '1', + }) =3D=3D 0 + assert conf.stdout_contains('expected_stdout') + assert conf.config_matches('expected_config') + + assert conf._run_conf('--savedefconfig=3Ddefconfig', dot_config=3D'con= fig', + out_file=3D'defconfig', + extra_env=3D{ + 'KCONFIG_WARN_CHANGED_INPUT': '1', + }) =3D=3D 0 + assert conf.stdout_contains('expected_stdout') + assert conf.config_matches('expected_defconfig') diff --git a/scripts/kconfig/tests/warn_changed_input/config b/scripts/kcon= fig/tests/warn_changed_input/config new file mode 100644 index 000000000000..dbe93ff26408 --- /dev/null +++ b/scripts/kconfig/tests/warn_changed_input/config @@ -0,0 +1,3 @@ +CONFIG_A=3Dy +CONFIG_NUM=3D30 +CONFIG_DUP=3Dy diff --git a/scripts/kconfig/tests/warn_changed_input/expected_config b/scr= ipts/kconfig/tests/warn_changed_input/expected_config new file mode 100644 index 000000000000..fe8bbec66c53 --- /dev/null +++ b/scripts/kconfig/tests/warn_changed_input/expected_config @@ -0,0 +1,6 @@ +# +# Automatically generated file; DO NOT EDIT. +# Main menu +# +# CONFIG_DEP is not set +CONFIG_NUM=3D20 diff --git a/scripts/kconfig/tests/warn_changed_input/expected_defconfig b/= scripts/kconfig/tests/warn_changed_input/expected_defconfig new file mode 100644 index 000000000000..af9e34851d2a --- /dev/null +++ b/scripts/kconfig/tests/warn_changed_input/expected_defconfig @@ -0,0 +1 @@ +CONFIG_NUM=3D20 diff --git a/scripts/kconfig/tests/warn_changed_input/expected_stdout b/scr= ipts/kconfig/tests/warn_changed_input/expected_stdout new file mode 100644 index 000000000000..9ec8446b4ac2 --- /dev/null +++ b/scripts/kconfig/tests/warn_changed_input/expected_stdout @@ -0,0 +1,4 @@ +warning: user-provided values changed by Kconfig: + CONFIG_A: y -> n + CONFIG_NUM: 30 -> 20 + CONFIG_DUP: y -> n --=20 2.50.1 (Apple Git-155)